Microsoft might be introducing application specific glass renderings. The color of the glass frame around a window can be changed in Vista, but the change is global to the system. The color of any particular window glass frame can not be set by choice. But, how about being able to change the color/opacity level of a the glass frame of any application through defined events or commands? According to a Patent number 7418668:

A method for changing a color value and/or level of opacity value of a glass appearance window frame for an application window is described. The method includes steps of determining a defined color value and a defined level of opacity value to apply to a glass appearance window frame and displaying the glass appearance window frame in accordance with the defined color value and the defined level of opacity value. A command may be received to apply the defined color value and the defined level of opacity value to the glass appearance window frame, thereby applying the defined color value and level of opacity value to the glass appearance window frame. Color values and/or level of opacity values may be changed automatically, be application specific, and/or be changed in response to receipt of an input from a user to change one or more portions of a default configuration.........Continue reading

^^ True.

"Performace and stability are being cosidered as main moto" \

rightly said Ramesh...We don't want any UI change but we want better performance in same configuration.